The present invention relates to a vaporizing device for CVD source materials for a solution or a liquid used for CVD (chemical vapor deposition) forming of dielectric films, ferroelectric films, electrodes or wiring materials used in semiconductor memories, system LSI, electrical devices and the like as well as to a CVD apparatus employing the same.
Rapid progresses are being made in integration of memory devices utilized in semiconductors, and it is the case with dynamic random access memories (DRAMs) that progresses in integration thereof resulted in bit numbers are four times the number they were three years ago. Such progresses were made for the aim of achieving high speed, low electric consumption or low cost of devices. However, no matter how much integration shall be improved, capacitors which are components of DRAMs still need to keep a specified capacity for securing reliability.
For this purpose, it is required to achieve thinning of film thickness of capacitor materials while limits were found in thinning of SiO.sub.2 which is a commonly used material so far. Therefore, in view of the fact that improvements in permittivity by using different materials make it possible to secure a certain capacity as well as thinning, studies are being made in which dielectric materials (materials of high permittivity) are used as capacitor materials for memory devices.
On the other hand, ferroelectric memories are being paid attention to as one form of nonvolatile memories which do not require electric power for maintenance of memories. Such memories are so arranged that polarization and inversion, which are material characteristics of ferroelectrics, are made to correspond to presence or absence of memories and are advantaged in that they are not only nonvolatile but also capable of presenting high-speed actions and high integration, depending on improvements in material characteristics.
On the other hand, it has been considered to employ Pt or Ru as materials for electrodes as components of such semiconductor chips, and to employ copper as materials for wiring instead of conventionally used aluminum for the purpose of decreasing occurrence of delays owing to low resistance (of achieving rapidness of operating speed).
Characteristics which are required for such materials for capacitors are that they are thin films presenting high permittivity and that their leak current is small, while it is additionally required for ferroelectric materials that they present polarizing characteristics. That is, as long as materials of high permittivity are used, it is required to form a film having a minimum thickness and to set the leak current thereof also to minimum. In general, an approximate target for development is favorably set to be a film thickness of not more than 1 nm based on SiO.sub.2 conversion and a leak current density of an order of not more than 10.sup.-8 A/cm.sup.2 when applying a voltage of 1.65V.
Materials for electrodes are further required to present low reactivity with the dielectric materials to be used in combination and to be capable of being easily processed, and materials for wiring are further required to present a resistivity which is smaller than that of conventionally used aluminum.
Further, for the purpose of forming a thin film above electrodes of DRAM capacitors or ferroelectric memory cells which are arranged in a stepped manner, or vice versa, for forming electrodes or wirings above such a thin film, it is of remarkable advantage in view of processing that film formation can be performed through CVD methods wherein materials present favorable adhesiveness to base materials of complicated shapes and mass production is enabled.
In view of these facts, it has been considered to form oxide group dielectric films through CVD film forming methods utilizing, as materials for capacitors as well as ferroelectric materials, tantalum oxide, lead zirconate titanate (PZT), lead lanthanum zirconate titanate (PLZT), strontium titanate (ST), barium titanate (BT), barium-strontium titanate (BST) or strontium-bismuth tantalunate (SBT). Further, materials for metallic electrodes for the oxide films might be Pt or Ru, materials for oxide group conductive electrodes RuO.sub.2 or SrRuO.sub.3, and materials for wiring Cu.
Since it is most advantageous to form films by using CVD methods, various CVD source materials for performing CVD film forming utilizing these materials have been developed, wherein many thereof are either in a liquid or in a solid state, and in case of solid source materials, these are used as source material solutions after being dissolved in suitable solvents.
For instance, Japanese Unexamined Patent Publication No. 158328/1994 discloses CVD source materials wherein conventional solid source materials are dissolved in an organic solvent of tetrahydrofuran (THF) to obtain a solution whereby vaporizing characteristics and compositional controllability have been remarkably improved, and Japanese Unexamined Patent Publication No. 310444/1994 further discloses a CVD apparatus.
However, while quite favorable vaporizing characteristics and compositional controllability could be achieved by using the above conventional source material solution in the above CVD apparatus, insufficient performance of the vaporizing device made it impossible to avoid generating of non-vaporized residues within a vaporizer or a spray nozzle thereof.
There was presented a drawback that such residues reached a CVD reactor in forms of particles to cause deficiencies in film forming and thus to degrade repeatability of film forming and that elongation of continuous operation time of the vaporizer was hindered thereby resulting in degradation of productivity for manufacturing memories.
That is, the above vaporizing device is so arranged that carburetion of source materials is performed by spraying solutions or liquid source materials into a heated vaporizer by means of a spray nozzle; however, since this mechanism is insufficient, thermal hysteresis of materials until vaporizing temperatures are reached become slacked, so that a part thereof is degraded by thermal decomposition or by formation of origomer before reaching into the vaporizer to thereby cause generation of non-vaporized residues.
On the other hand, since liquid source materials used for copper wirings are liable to cause thermal decomposition, generation of decompositions within the vaporizer was inevitable.
As discussed above, solutions or liquid source materials are generally liable to cause thermal decomposition, and the degree of decomposition was largely dependent on the performance of the vaporizing device.
The present invention has been made to solve these subjects, and it is an object thereof to obtain a vaporizing device for CVD source materials capable of restricting generation of non-vaporized residues and particles, and of achieving elongation of continuous operation time of the vaporizing device and decrease of occurrence of deficiencies in film forming.
It is further an object of the present invention to obtain a CVD apparatus capable of performing superior film forming by utilizing the above vaporizing device for CVD source materials to thereby improve productivity of manufacture of memories or the like.